The present invention relates to systems for protecting information and more particularly relates to systems for protecting information that is transmitted by means of a wired or wireless medium against unauthorized access.
One way of distributing information is to broadcast it, that is, to place the information on a medium from which the information can be received by any device that is connected to the medium. Television and radio are well-known broadcast media. If one wishes to make money by distributing information on a broadcast medium, there are a couple of alternatives. One alternative is to find sponsors to pay for broadcasting the information. A second is to permit access to the broadcast information only to those who have paid for it. This is generally done by broadcasting the information in scrambled form. Although any device that is connected to the medium can receive the scrambled information, only the devices of those users who have paid to have access to the information are able to descramble the information.
A service distribution organization, for example a CATV company or a satellite television company, often provides its subscribers with multiple services. Some of these services are sponsored and are transmitted in the clear. Others are paid for by the end user or subscriber and are scrambled. These services are called premium services. An example of a premium service would be a pay-per-view movie or pay-per-view sports event. These specific programs (i.e., the movie or sports event) may be broadcast to certain subscribers who wish to view, and have paid for, these programs. When the service distribution organization broadcasts a program, it scrambles the program to form a scrambled instance of the program. A scrambled instance contains instance data, which is the scrambled information making up the program.
The scrambled instance is broadcast over a transmission medium and is received at a large number of set top boxes. The function of a set top box is to determine whether the scrambled instance should be descrambled and, if so, to descramble it to produce a descrambled instance comprising the information making up the program. The program is then delivered to a television set for viewing by the subscriber.
Subscribers may purchase services on an event basis, and after a subscriber has purchased an event, the service distribution organization sends to the set top box belonging to the subscriber messages required to provide the authorization information (i.e., information necessary to descramble the scrambled instance) for the purchased premium service or event. If the authorization information indicates that the subscriber is entitled to watch the program of a scrambled instance, the set top box descrambles the scrambled instance to produce the program for viewing by the subscriber.
One drawback associated with this method is that the descrambling hardware is typically built into the set top box. The additional hardware adds cost to the set top box as well as to the system as a whole. Moreover, the additional hardware typically requires highly trained labor to keep the CATV system operational.
Additionally, typical CATV systems include an RF reverse path, which allows for the purchase of programs through the set top box at the time that the event is broadcast (i.e., impulse purchase of pay-per-view programs). In the absence of an RF reverse path, however, an alternate method is needed to allow for impulse purchasing of pay-per-view programs, or various other types of conditional access. This may be done via a phone line or other wireless connection. However, phone lines or wireless connections, and associated components, add to the complexity and cost of a system.
There is, therefore, a need in the industry for a simple and cost-effective method to accommodate impulse purchasing of pay-per-view programs, or various other types of conditional access.
A system and method are provided for controlling subscriber access to premium services in a conditional access system (e.g., a CATV system). Briefly described, the system includes, in one embodiment, an access device comprising a non-volatile memory having authorization information, a counter having a predetermined count, and a microprocessor configured to receive the authorization information from the memory. The microprocessor is further configured to receive an entitlement control message from a scrambled instance at an encryption period associated with the scrambled instance, and produce a control word from the authorization information and the entitlement control message at each encryption period. The microprocessor is further configured to decrement the counter at each encryption period in response to the generation of the control word.
The invention can also be seen as encompassing a method for descrambling a scrambled instance having contiguous scrambled sections. The method comprises the steps of descrambling a scrambled instance comprising contiguous scrambled sections, each section having an encryption period proportional to a predetermined encryption cycle rate, and decrementing a counter in response to the descrambling of each scrambled section.
Other systems, methods, features, and advantages of the invention will be or become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.